The Wireless Local Area Network (WLAN) and the cellular mobile communication network (cellular network for short) are two wireless communication technologies widely applied to the world at present. The WLAN mainly aims at a personal consumption electronics market and a broadband wireless access market for families and enterprises. The cellular network mainly aims to a telecom operator market and provides mobile communication service for the public. As intelligent mobiles are popularized on a large scale and the mobile internet is quickly developed, users need a wireless access network with high transmission speed more intensely. A 4th Generation (4G) network represented by a Long Term Evolution (LTE) technology is being gradually constructed and deployed. Compared with wide coverage of a 3rd Generation Partnership Project (3GPP) cellular mobile network, the WLAN places more emphasis on provision of low-mobility data services for mobile phones and the mobile internet in hot-spot regions.
In order to reasonably utilize network side resources and guarantee the service experience of the users, it is particularly important to select an appropriate access network. More terminals have an ability to access more access networks at the same time due to the popularisation and development of the intelligent terminals. How to select the most appropriate access network at appropriate time and at an appropriate place by the users so as to obtain an optimal network application experience is a problem on which an operator needs to focus. A 3GPP proposes a network selection mechanism based on Access Network Discovery Support Functions (ANDSF) is capable of selecting an access network according to factors such as a geographic position of a user, a load state of the access network and a selection preference of the user, providing an optimal network selection policy for a terminal, balancing the load state of the network, guaranteeing the quality of services, and improving the user experience.
In an Evolved Packet System (EPS) and an access network framework proposed by the existing 3GPP, the EPS supports intercommunication with a non-3GPP system, which is realized via S2a/b interfaces. An anchor point between a 3GPP system and the non-3GPP system is a Packet Data Network Gateway (PDN GW). The non-3GPP system can be divided into trusty non-3GPP Internet Protocol (IP) access and trustless non-3GPP IP access. The trusty non-3GPP IP access can be directly connected with the PDN GW via an S2a interface. The trustless non-3GPP IP access needs to be connected with the PDN GW via an Evolved Packet Data Gateway (ePDG), and an interface between the ePDG and the PDN GW is an S2b interface. User Equipment (UE) interacts with the ANDSF via an S14 interface. The S14 interface supports both a PULL mechanism (UE requesting) and a PUSH mechanism (network triggering), and is implemented over an IP layer. The ANDSF includes a data management and control function, and information including an intersystem mobility policy, access network discovery information and an intersystem routing policy can be provided as follows.
1) The intersystem mobility policy refers to a group of rules and preferences defined by the operator, and can influence an intersystem mobility decision. The UE decides whether intersystem mobility is intended to allow or limit and select a more preferred access network by using the intersystem mobility policy. The intersystem mobility policy should be provided for a mobile terminal based on user requesting or network triggering, and can be updated by the ANDSF. An access technology marked by the intersystem mobility policy or a specific access network having higher priority can be limited or allowed.
2) When the UE requests for network selection, the ANDSF can provide a group of effective access network lists surrounding the UE, the list including various pieces of access network technology information. The effective access technology information includes an access technology type (such as the WLAN and Worldwide Interoperability for Microwave Access (WiMAX)) and a wireless access network identifier (such as a Service Set Identifier (SSID) of the WLAN). In addition, there is also specific information of other technologies such as one or more carrier frequencies, and restraint conditions such as some conditions mark a moment at which provided access network information is effective. The UE should retain and use these pieces of access network information provided by the ANDSF until next updating information is received.
3) When the UE routes an IP service by simultaneously using a plurality of wireless interfaces, the ANDSF probably provides an intersystem routing policy list to the UE, and the UE can route the IP service via the interfaces simultaneously. The UE uses this policy to realize operator routing/offload priority, and decides when an access technology is limited to a specific IP service stream; and a specific principle is matched with the routed IP service, and the most appropriate access technology is selected. The intersystem mobility policy should be provided for the mobile terminal based on user requesting or network triggering, and can be updated by the ANDSF at the same time.
Only static information is defined by the ANDSF in a current standard. Since access network information in an access network information list stored in an ANDSF database cannot be dynamically updated, under some conditions that a certain access point is closed due to a fault or is no longer suitable for access of a new user due to over-large number of current users and over-high load, the information of these access points is invalid information. In order to avoid the conditions, after a user terminal obtains the access network information, it is necessary to scan the access network so as to determine current availability information of the network, thereby improving the switching delay, reducing the switching efficiency, and improving the power consumption of the user terminal.